The present invention relates to a method in which waste plastic material or waste rubber material is recycled so as to obtain hydrocarbon oil and an apparatus used for carrying out the method.
In present motor vehicles, a vehicle body panel, various interior parts, tires, etc. are formed by polymer such as plastic material or rubber material and ratio of plastic material or rubber material used for each motor vehicle has been raised gradually. Therefore, even if only one motor vehicle is scrapped after its service life, a considerable quantity of waste plastic material or waste rubber material is generated. Since a number of motor vehicles are scrapped every day at present, a total quantity of waste plastic material or waste rubber material is enormous.
Such waste plastic material or waste rubber material, which is produced in huge quantity only in connection with motor vehicles, is tested for various effective recycling purposes in various industrial fields including car industry. Furthermore, efforts for further promoting the recycling are being exerted. Under these circumstances, Japanese Patent Laid-Open Publication No. 63-178195 (1988) proposes, as one example of recycling of waste plastic material or waste rubber material, that hydrocarbon oil is produced from waste plastic material or waste rubber material and the produced hydrocarbon oil is used as fuel, etc.
In a known method of producing hydrocarbon oil from waste plastic material, the waste plastic material is subjected to thermal cracking so as to obtain thermal cracking gas and the thermal cracking gas is subjected to vapor phase catalytic cracking by using proper catalyst so as to obtain catalytic cracking gas and then, the catalytic cracking gas is cooled so as to obtain hydrocarbon oil having relatively low boiling point. For example, in a method disclosed in the above mentioned prior art document No. 63-178195 (1988), thermal cracking of the plastic material is performed in melt phase at a temperature of 390.degree. C. to 500.degree. C., while vapor phase catalytic cracking of the thermal cracking gas is performed at a temperature of 200.degree. C. to 350.degree. C. by using zeolite as the catalyst. As a result, low-boiling hydrocarbon oil containing 22 carbon atoms or less is obtained. This known method in which the hydrocarbon oil is obtained by thermal cracking, vapor phase catalytic cracking and cooling steps can be applied to not only waste plastic material but waste rubber material.
Meanwhile, in case thermal cracking of waste plastic material is performed at relatively high temperature, ratio of gaseous component increases and thus, recovery of desired low-boiling hydrocarbon oil drops. A countermeasure for eliminating this drawback is proposed in, for example, Japanese Patent Laid-Open Publication No. 52-144088 (1977) in which in order to set thermal cracking temperature relatively low, thermal cracking of the waste plastic material is performed in a state where mixture of the waste plastic material and aluminum chloride acting as catalyst is being stirred.
When the hydrocarbon oil is produced from waste plastic material or waste rubber material as described above, catalyst such as zeolite used for vapor phase catalytic cracking of the thermal cracking gas produced through thermal cracking of the waste plastic material or the waste rubber material is maintained at not more than a predetermined temperature lower than a temperature for thermal cracking of the waste plastic material or the waste rubber material so as to prevent a phenomenon in which heat deterioration of the catalyst leads to, for example, production of a large quantity of hydrocarbon gas. Therefore, the thermal cracking gas produced through thermal cracking of the waste plastic material or the waste rubber material is cooled by the catalyst during vapor phase catalytic cracking. Consequently, such a problem arises that heavy component (wax component) contained in the thermal cracking gas adheres to the catalyst, thereby resulting in drop of function of the catalyst. Meanwhile, the heavy component contained in the thermal cracking gas subjected to vapor phase catalytic cracking is mixed into the hydrocarbon oil obtained by vapor phase catalytic cracking, thereby undesirably resulting in deterioration of quality and drop of recovery of the finally recovered hydrocarbon oil.
Furthermore, when in order to set thermal cracking temperature relatively low, thermal cracking of the waste plastic material is performed in a state where mixture of the waste plastic material and aluminum chloride acting as catalyst is being stirred as described above, molten substance obtained by thermal cracking has relatively high viscosity and thus, such disadvantages are incurred that efficiency for stirring the mixture is not so high and the catalyst evaporates rapidly.